A 74-year-old man was playing poker with his neighbors when he noticed that he was having difficulty picking up his cards with his left hand. Determining that he was fatigued from his day of yard work, he went home and to bed. The next morning he staggered and nearly fell making his way to the bathroom. Concerned about her husband's condition his wife takes him to the emergency room. Neurological examination indicates that the man is unable to elevate and adduct his right eye; however, abduction and depression of his right eye is normal. The eye movement abnormalities in this patient are most indicative of which of the following?